This invention relates to carbonate polymer compositions containing additives which act as flame retardants together with an additive which improves processing stability.
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene, have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance, and excellent electrical properties are required.
Unfortunately, however, these polymers exhibit a brief but definite burning time when contacted with an open flame. More importantly, as is often the case, the carbonate polymers contain stabilizers and other additives which are often more combustible than the unmodified carbonate polymer. As a result, the modified carbonate polymers frequently exhibit substantially poorer resistance to combustion than does the unmodified carbonate polymer.
In attempts to increase the combustion resistance of carbonate polymers including the modified forms thereof, it has been a common practice to employ monomeric phosphites, phosphoric acid esters, thiophosphoric acid esters containing halogenated alkyl radicals and halogenated organic compounds into the carbonate polymer. However, in order to obtain any noticeable improvement in combustion resistance, these additives have been employed in such large quantities that they often adversely affect many of the desirable physical and mechanical properties of the carbonate polymer.
The use of aromatic sulfimides as flame retardants in carbonate polymers is suggested in U.S. Pat. No. 4,254,015 dated 3-3-81. However, it was found that while these additives are efficient as flame retardants they also adversely affect the processing stability of the carbonate polymers. In other words, during melt processing such as extruding into pellets there is a considerable lowering of the molecular weight.
The use of metal salts of inorganic acids such as sodium bisulfate as flame retardants is suggested in U.S. Pat. No. 4,486,560. However, this patent does not suggest the use of these compounds as processing aids.
The use of a metal salt of aromatic sulfonamides and a metal sulfate or bisulfate to provide flame retardant polycarbonates is disclosed in U.S. Pat. No. 4,532,284. However, this patent does not suggest the use of halogenated organic compounds and polytetrafluoroethylene and hence the polycarbonates prepared therein are not as flame retardant as is desired.